nearly as long as the shell. Thorax slenderly conical, rough, with straight outlines, and irregular, roundish pores, gradually increasing in size towards the mouth.
Dimensions.—Cephalis 0.01 diameter, thorax 0.09 long, 0.03 broad.
Habitat.—Indian Ocean (Zanzibar), depth 2200 fathoms (Pullen).
18. Sethoconus gracilis, Haeckel.
Cephalis small, subspherical, with few scarce pores, and a stout, pyramidal horn, of the same length. Thorax slenderly conical, three to four times as long as broad, with straight outlines, and very small and numerous circular pores of equal size.
Dimensions.—Cephalis 0.015 diameter, thorax 0.12 long, 0.04 broad.
Habitat.—Fossil in Barbados.
19. Sethoconus bimarginatus, n. sp. (Pl. 54, fig. 12).
Cephalis very small, subspherical, hyaline, without pores, with a rudimentary, conical horn of the same length. Thorax slenderly conical, three times as long as broad, with undulated, little convex outlines, and irregular, roundish, double-contoured pores, arranged in nine longitudinal series, markedly increasing in size towards the mouth.
Dimensions.—Cephalis 0.01 diameter, thorax 0.16 long, 0.05 broad.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
20. Sethoconus clathratus, Haeckel.
Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, three to four times as long as broad, smooth, with curved axis and small, regular, circular pores, nearly equal in size. This common species differs from all others of the genus by the curvation of the axis of the shell, which is more or less crescentic, or curved like a cowherd's horn; it may, therefore, represent a peculiar genus, Sethodrepanum.
Dimensions.—Cephalis 0.003 to 0.006 diameter, thorax 0.08 to 0.16 long, 0.03 to 0.05 broad.
Habitat.—Cosmopolitan; Atlantic, Pacific, many stations; fossil in Barbados and Sicily.
Subgenus 3. Phlebarachnium, Haeckel (et Cladarachnium, Haeckel), 1881,
Prodromus, p. 430.
Definition.—Cephalis small, with very small pores, and internal collar septum. Thorax spiny or thorny.
